Bimetallic actuator



Aug. 14, 1945. J. STRONG 2,382,182

BIMETALLIC ACTUATOR Filed April 12, 1940 5 mum mmj h ATTORNEYS Patented Aug. 14, 1945 BIMETALLIC ac'rua'roa Judson Strong, Great Neck, N. Y., assignor to The H. A. Wilson Company, Newark, N. 1., a corporation of New Jersey Application April 12, 194i), Serial'No. 329,249

3 Claims.

This invention relates to actuating or motionproducing devices and more particularly to a novel device of this character which operates on a temperature diiferential between different parts of the device. The new device may be manufactured at low cost and is of simple construction because of its inclusion of a bimetallic element as the operating member.

One feature of the invention resides in the provision of a novel actuating device whichoperates as the result of a difference between the temperature of a part of the device and the ambient temperature. A device made in accordance with the invention comprises'a strip of bimetal secured in a bowed form, preferably by means of a connection between the ends of the strip. Intermediate its ends, the strip is engaged by a heat conducting element which conducts heat to or away from the adjacent part 01' the strip so as to change the temperature of this part relative to the ambient temperature and the temperature of -the remote parts of the strip. As a result, the part of the strip contacting the heat conducting element assumes a more pronounced bow-shape and causes movement of the connected ends oi the strip. v The heat conductin element may be in the form of a heating medium or a cooling medium, depending on the arrangement of the diflerent metals in the bimetal. That is, if the metal having the higher coefllcient of expansion is on the convex side of the strip, then a heating medium is used to conduct heat locally to the part of the strip engaging the medium, but if the metal having the higher coeflicient of expansion is on the concave side of the strip, a cooling medium is used to conduct heat away from the adjacent part of the strip. In either case, the transfer of heat causesthe part of the strip adja cent the conducting medium to become more bowed so that the connecting means between the ends of the strip is moved relative to the affected part of the strip.

Another feature of the invention is in the provision of a novel actuating device which rolls automatically due to the action of a heat conducting element on a curved strip of bimetal. Preferably, the strip is secured at its ends so that it has a substantially uniform radius of curvature, and it is supported and adapted to rock on the heat conducting element. If the high expansion metal is on the convex side of the strip, the support is maintained at a temperature above the ambient temperature so that the part of the strip contacting the support is heated by conduction and assumes a more pronounced bow-shape,

with the result that the connected ends of the strip are elevated somewhat from the support. and the position of the center of gravit is changed. The strip is then caused to roll in one direction or the other, and as it rolls the bimetal disengaging the support cools so that it tends to straighten, while the bimetal moving progressively into engagement with the support becomes more bow-shaped under -the action of the heat. As a result of this progressive deflection of the bimetal, a bump or protrusion is caused to travel along the strip in the region of the support as the strip rolls so that when the rolling movement is finally arrested, the unbalanced condition of the strip tending to rock it in the opposite direction is accentuated. A reversal of the movement then takes place, accompanied by progressive defiection of the bimetal, and the strip rocks until it becomes sufilciently unbalanced to cause another reversal of its movement.

These and other features of the invention may be better understood by reference to the accompanying drawing, in which Fig. 1 is a front view of one form of the new actuating device, showing the device in static condition;

Fig. 2 is a side view of the device shown in Fig. 1;

Fig. 3 is a view similar to Fig. 1 showing the device in the initial stage of its oscillating movement;

Figs. 4, 5 and 6 are views similar to Figs. 1 and 3 showing different positions of the device during its oscillation, and

Fig. 7 is a sectional view of another form oi the actuating device.

While the new device may take various forms depending on the kind of motion desired, I have shown in Figs. 1 to 6, inclusive, a form suitable for producing an oscillating or rocking motion. Referring to Figs. 1 and 2, the device comprises a strip of bimetal Ill having its ends connected together by a cross member II which holds the strip substantially in the form of a semi-circle. Preferably, the strip III is relatively thin, for example, in the order of a few thousandths of an inch in thickness, so that it deflects readily under the action of heat, is sensitive to small temperature changes, and may be heated and cooled quickly. The strip is adapted to rock on a flat support I! and is suiiiciently wide to give the strip stability and enable it to remain upright on the support, The support i2 is made of a suitable heat conducting material, such as metal, glass, or the like, and may be provided with suitable means (not shown) for heating the support or for cooling it, depending on the arrangement of, the different metals in the strip Iii. More particularly, if'the metal having the higher coefficient of expansion is on the upper or concave surface of the strip, then the support I! is cooled below theambient temperature, but if the high expansion metal is on the lower or convex surface of the strip, the support I! is heated above the ambient temperature. In either case, the transfer of heat to or away from the part of the strip contacting the support causes this part to assume a more pronounced bow-shape due to the flexing of the affected bimetal.

The strip II, as shown, is arranged to actuate a display card it secured to the cross member II. The card it may have any suitable advertising matter or other indicia (not shown) arranged thereon.

when the temperature of the support I! is the same as the ambient temperature, the bimetallic strip II is heated equally throughout its length and assumes the static position of equilibrium shown in Fig. 1. In this position, the intermediate portion of the strip contacts the support, and the connecting member H holds the strip substantially in the form of a semicircle, although, depending on the weight of the connector ii and the card it and the stiffness of the bi metal, the part of the strip contacting the support may be more or less flattened by the weight which it sustains.

Assuming that the metal having the higher coeiiicient of expansion is on the lower or convex surface of the strip, heating of the support I! will cause the adjacent contacting part of the strip to flex under the action of the heat conducted thereto, whereby this part assumes a more pronounced bow shape, as shown at II, and acts to raise the connector Ii and therefore the center of gravity of the members II, II and ii. The strip II is then caused to roll in either one direction or the other, either as the result of an unbalanced condition developed by th raising of the center of gravity or due to the application of an external force. Assuming that the strip rolls to the left, the intermediate part is after disengaging the support I! cools due to the dissipation of heat in the surrounding atmosphere and tends to straighten. However, the metal moving into contact with the support I! is heated by conductionvfrom the support and, therefore, is caused to assume a more pronounced bow shape, as shown at it in Fig. 4. Thus, as the strip rolls, the bimetal is progressively heated by engagement with the support and progressively cooled after it disengages the support, so that a protrusion or bump is caused to travel along the strip in the region of its contact with the support.

This rolling of the strip away from its static position of equilibrium sets up an unbalanced force opposing the movement, and when this force is suflicient to arrest the movement, the strip rolls back toward the right and the action is reversed. As the strip rolls through its initial position, as shown in Fig. 5, the intermediate part II reengages the support and again deflects due to the conduction of heat thereto, and then,

as the inertia of the parts causes further rolling of the strip to the right, the part is again disengages the support, cools and tends to straighten, while the bimetal moving for the first time into contact with the support becomes more bowed under the action of the heat conducted thereto, as shown at II in Fig. 6. When the movement to the right is arrested by the unbalanced force opposing it, the strip rocks back tn the left again and the cycle is repeated. By reason of the progressive bowing and straightening of the bimetal adjacent the region of its contact with the support, the strip is caused to rock back and forth as long as the support If is heated to a higher temperature than the surrounding atmosphere.

While I am not prepared to explain definitely the mechanical action causing the continued rocking movement, I am of the opinion that the action is as follows: As the strip in rocks in one direction, to the left, for example, the bimetal moving into contact with the support I2 is heated by conduction from the support, but the effect of the conducted heat on the small area of himetal contacting the support is not instantaneous. This may be due at least in part to the fact that the heat impulse from the support is directed only on the lower or convex surface of the strip, and it takes a short time for the heat to diffuse into the bimetal. In any case, the affected bimetal does not undergo any substantial deflection until the rolling movement causes it to disengage the support. Accordingly, the protrusion or bump caused by the progressive heating and bowing of the bimetal lags slightly behind the region' of contact between the bimetal and the support, and this lagging protrusion acts to push the bimetal in the direction in which it is rolling. when the inertia of the moving parts and the actuating force incident to the progressive deflection of the bimetal are overcome by the unbalanced force tending to return the parts to their intermediate position, the motion is arrested and the strip rocks over the protrusion in the opposite direction, the protrusion again following the region of contact between the strip and the support.

For best results, the weight and arrangement of the parts carried by the strip ill should be correlated to the sensitivity of the bimetal so that the natural period of oscillation of the moving parts permits the protrusion resulting from progressive, thermostatic deflection of the bimetal to move along the strip at substantially the same rate as the angular movement of the strip, whereby the protrusion travels in the region of contact between the strip and the support. I have found that the frequency of the oscillations of the moving parts is substantially unaffected by changes in the diiferential between the temperature of the support and the ambient temperature, although the amplitude of the rocking movement increases with this temperature differential. Accordingly, the device may be used as a timing means, or for opening and closing a pair of contacts periodically. Also, I have found that the oscillating movement may be obtained efliciently with a small amount of heat by using two sources of heat, one near each end of the range of movement of the strips. By employing two heating sources so arranged, it is unnecessary to heat the entire surface of the support and the movement is obtained with a smaller consumption of heat. It will be apparent that the action of the device will be the same if the sup metal 20 held by a cross member 2| in a bowed form with the higher expanding metal on the convex side. The strip is mounted intermediate its ends on a dish-shaped diaphragm 22 made of heat conducting material, such as metal, and forming part of an enclosure for the strip. The enclosure, as shown, is constituted partly by the diaphragm 22 and partly by a support 23, such as a ceiling, to which the diaphragm is secured. Intermediate its ends, the cross member 2| carries a contact 24 coacting with a fixed contact 25 secured to the ceiling.

When the temperature outside the diaphragm 22 increases slowly, heat is transferred by convection from the diaphragm to the strip 20 at substantially the same rate that it is transmitted by conduction to the part of the strip contacting the diaphragm. Accordingly, the strip is heated substantially uniformly throughout its length and is held in the form of a static are by the cross member 2|. However, when the outside temperature increasesrapidly, the rate of heat transfer by conduction from the diaphragm 22 to the part of the strip contacting the diaphragm is much greater than that by convection from the diaphragm through the air in the enclosure to the side portions of the strip. As a result, the intermediate part of the strip is heated to a substantially higher temperature than the adjacent parts, and the strip flexes and tends to become parabolic, whereby the cross member II is moved upwardly and closes the contacts 24 and 25. When the rate of the temperature rise outside the enclosure decreases, the strip 20 becomes more evenly heated throughout and tends to return to its normal position, thereby moving the cross member downwardly and disengaging the contacts. The contacts 25 may be arranged to control a circuit (not shown) for actuating a fire alarm, a, sprinkler system, or the like.

It will be apparent that the actuating device of my invention is of simple construction and employs only a few moving parts. The device may be arranged to provide either a straight line I movement or a rocking movement, as desired,

but in either case it operates on a temperature differential between different parts of a bowed, bimetallic strip, which diflerential is produced by conduction of heat locally to or away from a part of the strip contacting a heat conducting medium.

While in the devices specifically described and illustrated herein a bump or protrusion occurs when a section of the bowed strip is heated by the support, it will be apparent that a flattening of a section of the strip may be obtained by arranging the strip with its high expanding metal on the convex or lower side and placing the strip on a support which is cooler than the ambient temperature or by arranging the strip with its high expanding metal on the concave or upper side and placing it on a support which is warmer than the ambient temperature. In certain devices, this flattening effect may be desired rather than the bowing eflect because of design or for other reasons. For example, in a rocking device which is operated by external means, such as electromagnets. etc, the flattening effect would disturb, retard or completely stop the rocking movement. Also, the flattening effect may be used to advantage in a rate of change thermostat in which a normally closed circuit is desired instead of a normally open circuit as shown in Fig. 7. When a normally closed circuit is desired, the bowed strip is arranged to hold the contacts 24 and 2! closed under normal conditions and to flatten when heated locally and thereby open the contacts.

I claim:

1. A thermal device comprisin a thin bimetallic thermal means, rigid means carried by said thermal means and secured to spaced points thereof and maintaining said points in predetermined relation with the portion of the thermal means between said points curved and with the convex side of said thermal means exposed, and said thermal device when cold having its center of gravity below and in a radius passing through the center of curvature of the thermal means whereby on disposing of the convex surface portion of the thermal means on a heated surface the heat causes a characteristic distortion of the thermal means momentarily at the place of contact with said heated surface and results in a shifting of the center of gravity of the device to one side or the other of said radial line to produce a rocking movement of the device.

2. A thermal device comprising a thin bimetallic thermal means, rigid means carried by said thermal means and secured to spaced points thereof and maintaining said points in predetermined relation with the portion of the thermal means between said points curved and with the convex side of said thermal means exposed, and said thermal device at room temperature having its center of gravity below and in a radius pass-.-

ing through the center of curvature of the thermal means whereby on disposing of the convex surface portion of the thermal means on a surface having a temperature substantially different from room temperature the temperature differential causes a characteristic distortion of the thermal means momentarily at the place of contact with said surface and results in a shifting of the center of gravity of the device to one side or the other of said radial line to produce a rocking movement of the device. 3. A thermal device comprising a strip of thermostatic bimetal and a rigid non-thermostatic member secured thereto at points spaced apart along the length of the strip and holding the strip permanently in a curved condition in which its convex side serves as a rocker for application to a surface having a temperature substantially different from room temperature and the center of gravity of the combined strip and member is below and in a radius passing through the center of curvature of the strip whereby the temperature differential causes a characteristic distortion of the portion of the bimetallic strip over the area adjacent to that in contact with said surface and thereby produces a rocking movement of the device upon the surface.

JUDSON STRONG. 

